Performance of QAM on a Hybrid Fiber-Coax CATV System

The digital system performance using 4 and 64 Quadrature Amplitude Modulation (QAM) was measured and analyzed in an operational CATV system. The effect of the various channel impairments on QAM transmission in both directions is shown in this paper. The resulting performance is found to vary with respect to time, to signal level, and to direction of transmission. In the forward path, the effect of background impairments varies with time and with signal power. In the return path, the effect of interferer-like impairments limits the system performance.